There have been a number of proposals to use nuclear magnetic resonance (NMR) variously referred to as magnetic resonance imaging (MRI) for examining a flowing stream of fluid in the pipeline. The fluid may be liquid hydrocarbon or a mixture of hydrocarbon and aqueous phases, such as the flow produced from an underground reservoir. Some gas may be present in the fluid. Use of NMR for such flow measuring/monitoring was disclosed in U.S. Pat. Nos. 3,191,119 and 3,419,715 and has been the subject of other patents since then, including U.S. Pat. Nos. 6,046,587, 7,501,819, 7,852,074 and 7,872,474. In a number of these documents the apparatus is shown as having a pipeline which passes through the magnetic field used (together with radiofrequency signals) to induce and observe magnetic resonance within the pipeline. The apparatus may also include polarizing magnets upstream of the magnets used to bring about magnetic resonance. NMR apparatus such as described in these documents has the attraction that it can be carried out without requiring any parts to be placed in the pipeline.